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Add support for display: contents style #47035

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Summary:
This PR adds support for display: contents style by effectively skipping nodes with display: contents set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - display: contents allows nodes to be skipped, i.e.:

<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>

node3 will be laid out as if it were a child of node1.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces LayoutableChildren::Iterator which can traverse the subtree of a given node in a way that nodes with display: contents are replaced with their concrete children.

A tree like this:

flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:https://github.com/facebook/yoga/issues/050
    style C fill:https://github.com/facebook/yoga/issues/050
    style D fill:https://github.com/facebook/yoga/issues/050
    style H fill:https://github.com/facebook/yoga/issues/050
    style I fill:https://github.com/facebook/yoga/issues/050
Loading

would be laid out as if the green nodes (ones with display: contents) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many display: contents nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is cleanupContentsNodesRecursively. Since nodes with display: contents would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested contents nodes, would not be cloned, breaking doesOwn relation. All of this is handled in the new method which clones contents nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

X-link: facebook/yoga#1726

Differential Revision: D64404340

Pulled By: NickGerleman

@facebook-github-bot facebook-github-bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Oct 15, 2024
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This pull request was exported from Phabricator. Differential Revision: D64404340

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 15, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
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This pull request was exported from Phabricator. Differential Revision: D64404340

@j-piasecki
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I've updated the original PR to be based on this one: #46584. Feel free to cherry-pick the changes if it makes things easier.

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 18, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
Contributor

This pull request was exported from Phabricator. Differential Revision: D64404340

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 18, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
Contributor

This pull request was exported from Phabricator. Differential Revision: D64404340

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 18, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
Contributor

This pull request was exported from Phabricator. Differential Revision: D64404340

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 18, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
Contributor

This pull request was exported from Phabricator. Differential Revision: D64404340

NickGerleman pushed a commit to NickGerleman/react-native that referenced this pull request Oct 18, 2024
Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
Contributor

This pull request was exported from Phabricator. Differential Revision: D64404340

Summary:


This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Differential Revision: D64404340

Pulled By: NickGerleman
@facebook-github-bot
Copy link
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This pull request was exported from Phabricator. Differential Revision: D64404340

@@ -0,0 +1,150 @@
/*
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Hey @j-piasecki this is super cool love that you are contributing here!! My one bit of feedback is can we write tests for this class by itself? Meaning not relying on e2e layout conformance to test this indirectly? That way we can test specific node structures and how we expect to iterate over them

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To clarify, that one would be on Yoga side facebook/yoga#1726

But I don’t think that has to block merging this. Could be a separate PR.

facebook-github-bot pushed a commit to facebook/yoga that referenced this pull request Oct 19, 2024
Summary:
X-link: facebook/react-native#47035

This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:#50
    style C fill:#50
    style D fill:#50
    style H fill:#50
    style I fill:#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on #1725

Changelog: [Internal]

Pull Request resolved: #1726

Test Plan: Added tests for `display: contents` based on existing tests for `display: none` and ensured that all the tests were passing.

Reviewed By: joevilches

Differential Revision: D64404340

Pulled By: NickGerleman

fbshipit-source-id: f6f6e9a6fad82873f18c8a0ead58aad897df5d09
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@NickGerleman merged this pull request in e5296cf.

@facebook-github-bot facebook-github-bot added the Merged This PR has been merged. label Oct 19, 2024
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This pull request was successfully merged by @j-piasecki in e5296cf

When will my fix make it into a release? | How to file a pick request?

facebook-github-bot pushed a commit to facebook/litho that referenced this pull request Oct 19, 2024
Summary:
X-link: facebook/react-native#47035

This PR adds support for `display: contents` style by effectively skipping nodes with `display: contents` set during layout.

This required changes in the logic related to children traversal - before this PR a node would be always laid out in the context of its direct parent. After this PR that assumption is no longer true - `display: contents` allows nodes to be skipped, i.e.:

```html
<div id="node1">
  <div id="node2" style="display: contents;">
    <div id="node3" />
  </div>
</div>
```

`node3` will be laid out as if it were a child of `node1`.

Because of this, iterating over direct children of a node is no longer correct to achieve the correct layout. This PR introduces `LayoutableChildren::Iterator` which can traverse the subtree of a given node in a way that nodes with `display: contents` are replaced with their concrete children.

A tree like this:
```mermaid
flowchart TD
    A((A))
    B((B))
    C((C))
    D((D))
    E((E))
    F((F))
    G((G))
    H((H))
    I((I))
    J((J))

    A --> B
    A --> C
    B --> D
    B --> E
    C --> F
    D --> G
    F --> H
    G --> I
    H --> J

    style B fill:facebook/yoga#50
    style C fill:facebook/yoga#50
    style D fill:facebook/yoga#50
    style H fill:facebook/yoga#50
    style I fill:facebook/yoga#50
```

would be laid out as if the green nodes (ones with `display: contents`) did not exist. It also changes the logic where children were accessed by index to use the iterator instead as random access would be non-trivial to implement and it's not really necessary - the iteration was always sequential and indices were only used as boundaries.

There's one place where knowledge of layoutable children is required to calculate the gap. An optimization for this is for a node to keep a counter of how many `display: contents` nodes are its children. If there are none, a short path of just returning the size of the children vector can be taken, otherwise it needs to iterate over layoutable children and count them, since the structure may be complex.

One more major change this PR introduces is `cleanupContentsNodesRecursively`. Since nodes with `display: contents` would be entirely skipped during the layout pass, they would keep previous metrics, would be kept as dirty, and, in the case of nested `contents` nodes, would not be cloned, breaking `doesOwn` relation. All of this is handled in the new method which clones `contents` nodes recursively, sets empty layout, and marks them as clean and having a new layout so that it can be used on the React Native side.

Relies on facebook/yoga#1725

Changelog: [Internal]

X-link: facebook/yoga#1726

Reviewed By: joevilches

Differential Revision: D64404340

Pulled By: NickGerleman

fbshipit-source-id: f6f6e9a6fad82873f18c8a0ead58aad897df5d09
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